Instead, state contractors will be allowed to fill the old passage with rubble when the Alaskan Way Viaduct is demolished next year, according to a state-city agreement.

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But council members heard estimates as high as $100 million to reinforce the cut-and-cover passageway to modern seismic codes and do utility work. Even a bus-layover space might require $75 million, said Councilmember Mike O’Brien, chairman of the Sustainability and Transportation Committee.

Voting against were Councilmembers Debora Juárez and Sally Bagshaw, although Bagshaw said her vote was mostly symbolic, because she became convinced preservation is not affordable.

“The visions that you came up with struck me as ranging from brilliant, to economic-development opportunities, to fanciful. That said, I feel we’re a little too late,” Bagshaw said.

She effusively praised citizen-activists and encouraged them to work on a two-acre parcel at the old tunnel’s south end. After the last viaduct span is removed there, the state will plant grass on a steep hillside, then turn the site over to Seattle. The triangular piece may become a park, affordable housing or a community center, Bagshaw said.

Supporters of Recharge the Battery made last-ditch comments at Monday’s council meeting, to no avail. They pleaded with the council to think ahead two decades, and not squander the space below street level.

“I can’t imagine this tunnel disappearing from this city,” said Seattle architect David Miller, who recalled driving through and noticing an “inherent beauty” in the 1952-vintage structure. “It has latent potential for re-use.”

A column last winter by Seattle Times writer Danny Westneat suggested making it a local passage for buses or cars to miss Belltown traffic, an idea Bagshaw mentioned that also didn’t endure.

The Battery Street Tunnel’s demise is prompted by the new Highway 99 tunnel, to open this fall from Sodo to South Lake Union, with no midtown or Belltown exits. The new tunnel is opening about three years late.

The Washington State Department of Transportation is expected to receive bids and set its final costs in May for the old-tunnel decommissioning, which includes relocations or reinforcing of electric, water and sewer utilities.